Compacting machines or compactors are commonly used to compact work materials (such as soil, gravel, asphalt, landfill trash) to a desired density while constructing buildings, roads, parking lots, and other structures. In addition, compactors are often used to compact recently moved and/or relatively soft materials at mining sites and landfills. The process often requires a plurality of passes over the work material to reach the desired density.
Various types of compactors are known in the art. Some compactors include a rotatable roller drum that may be rolled over the surface to compress the material underneath. In addition to utilizing the weight of the roller to provide the compressive forces that compact the material, some compactors are configured to also induce a vibratory force to the surface. The vibratory forces assist in compacting the surface into a dense mass. To generate the vibratory forces one or more weights or masses may be disposed inside the roller at a position that is off center from the axis line around which the roller rotates. As the roller rotates, the position of the masses induce oscillatory or vibrational forces to the roller that are imparted to the surface being compacted.
Determining whether the desired level of compaction has been reached for the surface material being compacted may be estimated in a variety of manners. In some instances, the compaction may be approximated by compaction measurement system that measures the amount of power required to move the compactor along the surface of a work site. The compaction measurement system may determine a state of compaction relative to an absolute scale or a maximum amount of compaction. Data for compaction measurements may be obtained when the compactor moves in forward drive over a surface area and when the compactor moves in reverse drive over the same surface area. Sometimes the compaction measurements obtained on-site in forward drive and obtained in reverse drive are not the same for material with the same stiffness. It has been theorized that this may be due to a variety of causes, including machine calibration, roller bow wave, moisture content of surface material, and/or roller following versus roller leading through surface material.
U.S. Publication No. 2009/0108300 published Aug. 27, 2009 discloses an apparatus for controlling the compactive effort delivered to a soil by a compaction unit based on measured soil compaction. While this system may be beneficial, it does not address the sensitivity of soil compaction measurements to the direction of movement of the compactor. A better system is needed to calibrate the displayed compaction measurement for work site conditions.